The production of high viscosity hydrocarbons presents significant challenges. Extraction of high viscosity hydrocarbons is typically difficult due to the relative immobility of the high viscosity hydrocarbons. For example, some heavy crude oils, such as bitumen, are highly viscous and therefore immobile at the initial viscosity of the heavy oil at reservoir temperature and pressure. Indeed, such heavy oils may be quite thick and have a consistency similar to that of peanut butter or heavy tars, making their extraction from reservoirs especially challenging.
Conventional approaches to recovering such heavy oils often focus on methods for lowering the viscosity of the heavy oil such as by heating the reservoir so that the heavy oil may be more easily produced from the reservoir. Commonly used thermal recovery techniques include a number of reservoir heating methods, such as steam flooding, cyclic steam stimulation, and Steam Assisted Gravity Drainage (SAGD).
To generate the heat required by conventional thermal technologies, these conventional methods typically use combustion devices to produce the required heat. Unfortunately, these combustion devices produce substantial amounts of greenhouse gases, which are often vented to atmosphere. The accumulation of greenhouse gases such as carbon dioxide in the atmosphere is known to contribute to acid rain, ocean acidification, and global warming due to the greenhouse effect. Additionally, existing and proposed regulations encourage the reduction of carbon emissions or the carbon dioxide capture. Thus, capturing carbon dioxide remains a continuing interest due to environmental and regulatory concerns.
While technologies exist and are being further developed to capture or sequester carbon dioxide, these technologies are inefficient and often uneconomical. Examples of carbon dioxide capture processes include chemical absorption methods and carbon dioxide scrubbing processes. Capturing carbon dioxide from flue gas of traditional boilers often requires complex separation equipment to separate the carbon dioxide from the flue gas. Moreover, flue gas is typically produced at near atmospheric pressure, requiring expensive compression equipment to compress the carbon dioxide sufficiently so that it may be introduced into the appropriate capture or sequestration process. Flue gas from traditional boilers contains significant amounts of nitrogen. This presence of a significant amount of nitrogen in the flue gas dramatically increases the capital and operating costs of treating the flue gas due to the need for compressing the sheer quantity of nitrogen present in the flue gas.
Where air is used as the oxidant to the direct steam generator, the exhaust gas will necessarily contain significant amounts of nitrogen. In addition to the presence of nitrogen in the flue gas, direct steam generators also necessarily combine steam with the flue gas. Where it is desired to use the steam thus generated for enhancement of heavy oil recovery, the inability to feasibly separate the exhaust gas from the steam is particularly problematic with this nitrogen-laden steam where reservoirs are negatively impacted by nitrogen. Therefore, using steam produced by direct steam generators may be disadvantageous where it is desired to inject steam into a subterranean formation without one or more components of the exhaust gas such as nitrogen. Additionally, direct steam generators do not offer the ability to control or limit the amount of carbon dioxide that is combined
Thus, traditional combustion technologies suffer from one or more disadvantages including low pressure output which complicates carbon dioxide capture or sequestration, and in some cases, the failure to economically separate carbon dioxide from nitrogen and other components in the flue gas for efficient carbon dioxide capture. Additionally, in the case of direct steam generators, the failure to adequately segregate carbon dioxide from the output of traditional combustion technologies results in an inability to control or limit the amount of carbon dioxide introduced with steam to a subterranean formation. Often, it may be desired to use some amount of carbon dioxide as a tertiary recovery solvent to enhance heavy oil recovery, but the carbon dioxide is often inextricably mixed with large amounts of nitrogen which may negatively impact heavy oil recovery. Thus, operators are prevented from using such carbon dioxide streams to enhance heavy oil recovery due to nitrogen contamination.
While separation processes exist to recover carbon dioxide from flue gas or from the output of direct steam generators, these conventional technologies, such as cryogenic separation plants, are inefficient and suffer from high capital and operating costs. Moreover, such conventional technologies typically employ noxious or environmentally unfriendly solvents.
One alternative to traditional boilers to avoid problems posed by large amounts of nitrogen in the flue gas is to use an oxy-fired boiler. Oxy-fired boilers use oxygen in lieu of air as the source of oxidation. Hence, the combustion product of an oxy-fired boiler is devoid of nitrogen. Accordingly, the combusted fuel mainly comprises carbon dioxide and steam and is therefore much more easily processed to capture or sequester the carbon dioxide. Unfortunately, oxy-fired boilers require oxygen as the oxidation source which is not only costly but also demands significant upfront treatment to separate oxygen from air, typically using inefficient and costly cryogenic air separation processes.
For all of these reasons, traditional combustion technologies are not conducive to efficient carbon dioxide capture and sequestration. Accordingly, conventional thermal recovery techniques, such as SAGD, suffer from poor carbon dioxide footprints. That is, conventional thermal recovery techniques are poorly designed for subsequent carbon dioxide capture or sequestration. Indeed, in some cases, these thermal recovery techniques are so inefficient that they are often not economically viable for recovering heavy crude oil.
Accordingly, there is a need for enhanced heavy oil recovery methods that address one or more of the disadvantages of the prior art.